1. Field of the Invention
The present invention relates to a wavelength-conversion type light emitting diode (LED), more specifically to a white LED used to illuminate a subject when photographing the subject with a camera which is installed in an electronics device such as a mobile phone.
2. Description of Related Art
Recently, there has been an accelerated multifunctionization of mobile electronics devices such as mobile phones; in particular, mobile phones in which digital cameras are installed have become widely used. Furthermore, mobile phones including an electric flash structure for outputting flash light for photography have been proposed (see, for reference, Japanese Patent Laid-Open 2004-317891, page 3, FIG. 12). Here, refer to FIG. 19, the electric flash structure of a conventional mobile phone includes an electric flash emission part 105 which has a printed substrate 107, a white LED 111 mounted on the printed subsrate 107 and emitting white light, an electric flash emission lens 112, and a light shielding holder 113 for holding the electric flash emission lens 112 in position to engage an upper case 103 of the mobile phone and guides light emitted from the white LED 111 to the electric flash emission lens 112 without leakage.
The white LED 111 acts as a light source of the electric flash emission part 105, and a surface mount type LED for converting blue light into white light is, for example, used (see, for reference, Japanese patent Laid-Open 2001-7405, pages 3 and 4, FIG. 2).
FIG. 20 illustrates one example of a white LED used in the above-mentioned electric flash device. The white LED 11 shown in FIG. 20 includes a rectangular glass epoxy substrate 12, a pair of electrodes (cathode electrode 13 and anode electrode 14) patterned on the glass epoxy substrate 12, an LED element 20 mounted on a central portion of an upper surface of the glass epoxy substrate 12, a fluorescent material-containing layer 21 applied on a back surface of the LED element 20, bonding wires 27 and 28 for connecting the LED element 20 and the pair of electrodes 13, 14, respectively, and a cuboid-shaped translucent sealing resin 19 for sealing an upper portion of the LED element 20.
The white LED 11 is heated at about 240° C. in a reflow device using an infrared radiation and heated air system and surface mounted on a mother board by fixing lower surfaces of the pair of electrodes 13 and 14 to printed wirings 16 and 17 formed on the mother board 15 through solder 18.
Meanwhile, the fluorescent material-containing layer 21 applied to the back surface of the LED element 20 includes an adhesive base with an appropriate amount of fluorescent material which is uniformly dispersed in the adhesive. The back surface of the LED element 20 is fixed to the upper surface of the glass epoxy substrate 12 by a heat-hardening adhesive. The fluorescent material is excited by light emitted from the LED element 20, thus converting short-wavelength visible light into long-wavelength visible light.
For example, an yttrium compound or the like may be used as the fluorescent material.
Moreover, if the LED element 20 is a blue LED element including, for example, a gallium nitride based compound semiconductor, blue light is emitted from the blue LED element upwardly, downwardly and laterally. In this case, a portion of the blue light directed in a downward direction hits and excites the fluorescent material dispersed in the fluorescent material-containing layer 21, and is converted in wavelength into yellow light. The yellow light is emitted in all directions. The emitted yellow light is mixed with blue light 31 directed from the LED element 20 upwardly and laterally so that white light can be emitted.
However, a size of the above-mentioned surface mount type LED is limited by the design of a belonging electronics device, in particular, the thickness, of a case of an electronics device in which the LED is mounted. Therefore, LEDs installed in electronics devices are produced in various sizes according to designs, and also it is required to prepare additional parts such as spacers for fine adjustment. Accordingly, there is a problem that this results in troublesome work and very high cost.
In addition, because a process in which an LED is heated in the reflow device and mounted on a mother board of an electronics device by soldering is required for a surface mount type LED, there is a problem that the LED element itself and other parts used for the LED need to be heat resistant.
Furthermore, when the LED passes through the reflow process, there is a problem that separation of the substrate and the translucent sealing resin at the surface boundary thereof and disconnection of the bonding wires occur easily, thereby reducing reliability, stability, and so on.